Since CO2 was mainly blamed for global warming, there have been attempts to minimize CO2 emission through an international convention or the like. Along with such an international movement, research and development on fuel which can emit less CO2 with higher efficiency using the same fossil fuel has been conducted. Also, research and development on a method of efficiently capturing CO2 generated from factories or power plants using fossil fuels and separately storing or reusing carbon dioxide has been continuously conducted.
The methods of capturing carbon dioxide can be roughly classified into three methods: a chemical absorption method using a liquid desiccant; a physical adsorption method using a solid material; and a separation method using a film. The chemical absorption method using a liquid desiccant such as alkanol amine has been regarded as a very excellent capturing method in terms of economic feasibility or application of a process. However, the biggest problem of the conventional process using alkanol amine as a desiccant is that although it is easy to capture alkanol amine since it can be chemically strongly bonded to CO2, a recovering process for separating these two substances after capturing requires a high temperature, i.e. high energy, and alkanol amine is decomposed during the high-temperature recovering process, resulting in sharp deterioration in performance of the desiccant. Therefore, in order to uniformly maintain the amount of the desiccant during the whole process, it is necessary to continuously supply the desiccant in an amount as much as the amount of the decomposed and consumed desiccant.
By way of example, as for mono-ethanol-amine (MEA) having high industrial applicability, an amine functional group of MEA is chemically strongly bonded to CO2, and, thus, a high temperature of 100° C. or more is needed to separate these two substances after capturing and MEA needs to be continuously supplied in an amount as much as the amount of MEA decomposed and consumed during the capturing process [J. Davis and G. T. Rochelle, Energy Procedia, 1, 327 (2009)]. Further, MEA is highly reactive, and, thus, MEA primarily erodes a container surface and iron ions or radicals generated on the container surface cause decomposition of the desiccant. Then, decomposition products generated at the beginning cause additional reactions with oxygen, so that various kinds of organic oxides may be formed and the decomposition of MEA may be accelerated [S. Chi and G. T. Rochelle, Ind. Eng. Chem. Res., 41, 4178 (2002)].
Therefore, in order to efficiently capture and recover carbon dioxide included in an exhaust gas using the chemical absorption method, it is necessary to develop a novel desiccant having the following characteristics: 1) being not easily oxidized in the air; 2) being able to easily adsorb CO2 even at a low temperature; 3) being able to easily desorb CO2 from a compound capturing CO2 at a relatively low temperature of 100° C. or less; 4) having a very low steam pressure; and 5) being not decomposed at a recovering temperature for desorption.